1. Field of the Invention
The present invention relates to high strength, low ductility nickel base alloys and, more particularly, to processes for fabricating these alloys into useful article shapes.
2. Description of the Prior Art
In the gas turbine engine industry, to which the invention has particular application, the engine design criteria require the use of alloys having good high temperature strength and oxidation resistance. In response to the need, a number of nickel base alloys have been developed and used. Unfortunately, however, while the high strength demands have been satisfied, they have generally been achieved only at the expense of alloy fabricability, and in the manufacture of jet engines comprising thousands of individual parts of intricate shape formed to close tolerance, fabricability of the alloy is a major factor in determining the extent of its utility.
The Moore and Athey patent, U.S. Pat. No. 3,519,503, of common assignee herewith represents a significant advance in the art of fabricating high strength, low ductility alloys commonly used in gas turbine engines, especially nickel and cobalt base alloys. According to the process described therein, a high strength, low ductility alloy is extruded or otherwise compressively worked at an elevated temperature below the recrystallization temperature to refine the grain structure and place the alloy in a temporary condition of low strength and high ductility, a so-called superplastic condition. Thereafter, the alloy in the temporary superplastic condition is isothermally forged to desired shape in hot dies at a temperature below the recrystallization temperature while substantial grain growth is inhibited. The shaped alloy is finally returned to its original high strength, low ductility condition by conventional heat treatment. Other patents relating to this fabricating process are U.S. Pat. Nos. 3,698,219 and 3,987,658, both of common assignee herewith.
In fabricating certain engine components, specifically engine discs made of IN100, by the patented process, it has been found desirable to modify the alloy composition somewhat so that an optimum wrought component is produced. The Cox et al patent, U.S. Pat. No. 3,843,421, of common assignee with the present invention describes such a modified IN100 alloy composition especially tailored for use in the patented fabricating process.